1. Field of the Invention
The present invention relates to a shield tunneling machine which is adapted to efficiently excavate the ground composed of all types of soil, such as a rock mass layer, a boulder layer, or a clay or cohesive soil layer.
2. Description of the Prior Art
A semi-shield method is used for laying conduits, in which the conduits are laid under the ground by interconnected pipes, such as Hume pipes, after excavating the ground with an excavator or a shield tunneling machine. However, conventional shield tunneling machines adapted for ground excavation do not have gravel crushing means, and which a cutter head or a front disc cutter thereof, is provided with small hole so that the size of the gravel taken into the shield body is limited within a given amount by the small holes. For this reason, the gravel must be broken down into sail sizes by roller bits mounted on the front disc cutter so that the propulsion of the shield tunneling machine cannot be effective. Further, when excavating cohesive soil, accidents frequently occur when the small holes become clogged making excavation impossible.
The present inventor has invented a shield propelling machine which is disclosed in Provisional Patent Publication Application No. 242295 of 1985. The disclosed shield tunneling machine comprises a shield body, a conical inner surface formed on the front of the shield tunneling machine, wherein the conical inner surface defines a conical chamber having a bore which gradually converges rearward, a partition wall formed on the shield machine behind the conical inner surface, a shaft an end of which is rotatably supported by a bearing provided on the partition wall and the other end of which is rotatably supported by a bearing provided on the front portion of the shield body, a tapered consolidation head, and a conical rotor mounted on the shaft so as to be eccentrically rotatable about the center axis of the shield body. A boss is fixed to the front end of the shaft and spokes extending radially from the boss are provided on the shaft. Bits and chips are disposed on the spokes.
The above-mentioned shield propelling machine is designed to be used for excavating the ground composed of a cohesive soil layer, earth layer, and sand layer, in which the ground is excavated by bits and chips. Excavated earth is taken into the chamber defined by the conical surface at the front of the shield tunneling body, and consolidated by the conical rotor eccentrically rotated about the center axis of the shield body in cooperation with the conical surface. Consolidated earth is pushed relatively rearward with the propulsion of the shield tunneling machine, mixed with water or muddy water in a water chamber following the rear portion of a chamber defined by the conical surface, and then exhausted through a pipe arranged in the shield body to the outside of the starting shaft.
However, there are instances where the ground to be excavated is composed of a monosoil layer. There are many instances in which gravel of a variety of sizes are contained in the soil layers. In the above-mentioned machine, large size gravel is introduced between the conical surface of the shield body and the conical rotor eccentrically rotated about the center axis of the shield body, and gravel is crushed by forces acting on the gravel which are imposed by the conical rotor eccentrically being rotated about the center axis of the shield body.
In crushing gravel, it is preferable that the conical rotor rotate at high revolutions. For this reason, the above-mentioned shield tunneling machine is constructed in such a manner that a crank shaft, for eccentrically rotating the conical rotor, and the conical rotor, be driven through an epicyclic mechanism so that the number of revolutions of the conical rotor is increased. In addition, the conical rotor is connected with an independent drive motor so the that number of eccentric revolutions of the conical cutter can be increased regardless of the number of revolutions of the cutter (spokes with bits and chips).
Using the above-mentioned shield tunneling machine, the ground can be excavated by crushing gravel and discharging crushed gravel with muck through a discharge pipe to a rear area of the machine. However, in the above-mentioned shield propelling machine, the cutter includes bits or chips, it is necessary that the number of revolutions of the cutter be controlled to lower velocity, in order to effectively excavate the ground. To control the cutter velocity at a lower velocity impairs the efficiency of crushing gravel by the conical rotors in cooperation with the conical surface of the shield body. Accordingly, in order to secure the proper number of revolutions of the conical rotor, it is necessary to mount a planetary gear mechanism or an independent drive on the shield tunneling machine. As such, the structure of the machine is complicated.